The present invention relates to the kinematics of an air-intake flap for aircraft engines and more particularly the invention relates to attenuation of unwanted movement of such a flap at a secondary air intake opening in an aircraft engine.
High speed - high performance aircrafts usually have a primary air intake for each jet engine as well as a secondary or auxiliary air intake. This secondary air intake may be established and defined by slots or an opening covered by a flap but being opened during take-off and low speed cruising. This way additional cross-sectional area is made available for the air intake.
It was found that a so-called hammershock is produced in the air intake duct of an engine of a supersonic aircraft. The hammershock is a strong pressure wave resulting from flow irregularities at the engine's compressor and propagating therefrom in the air intake duct and in upstream direction. This hammershock is not just produced during high speeds, but occurs during slow speed cruising when the secondary air intake flaps are open. Accordingly, the pressure shock waves may cause the flap to be slammed shut at such a force that the air intake structure may well be damaged. Thus, it is necessary to attenuate any accellerated movement of such a flap.
Upon considering the problem, it has to be observed, that the shock wave resulting from the hammershock is less effective for fully open than for partially open air intake. The needed attenuation of the flap movement is, therefore, dependent upon the respective flap position.